This invention relates to dimensionally stable urea-formaldehyde foams, and more particularly to a method of modifying the conventional foam preparation to increase dimensional stability by the continuous admixing of a concentrated aqueous suspension of substantially un-ionized, linearly shaped, refractory particles, with fluid urea-formaldehyde foam containing ionized mineral acid. Such foams are used for heat and sound insulation in commercial and residential buildings where foam stability over long periods of time is essential.
Urea-formaldehyde foams after curing and drying are relatively light weight, and possess good heat and sound insulating properties. The foams are normally applied as a wet, partially cured, fluid froth which flows into and accurately fills areas or cavities to be insulated. The prior art has reported solution to many of the problems relating to application, such as production of uniform foam cell size and constant composition of the resin-curing agent blend. The excellent insulating properties, the relatively low cost, and the ease and accuracy of application are factors which should allow urea-formaldehyde foams to become a major commercial insulation material.
Unfortunately, urea-formaldehyde foams developed to date and reported in the prior art do not have the integrity required for commercial utility. Integrity is used here to indicate an ability to remain constant and unchanged throughout long periods of use as insulation. The prior art foams have lacked both physical and chemical integrity under normal use conditions. That is, the physical size, shape, contiguality, appearance, crystallinity, and the chemical composition of the urea-formaldehyde foams have changed significantly to the detriment of their insulating effectiveness. These conventionally prepared urea-formaldehyde foams, therefore, produce inferior insulation after the foams have lost their physical and chemical integrity.
Copending U.S. application Ser. No. 761,321 by this inventor, filed the same day as this application, discloses that chemical integrity of urea-formaldehyde foams may be preserved through long periods of use by modification of a partially cured urea-formaldehyde resin by acid catalyzed reaction with a water soluble dialdehyde, such as glyoxal, and supplemental urea. Although preservation of the chemical integrity of the foam provides a significant improvement in the utility of urea-formaldehyde foams, it does not provide a completely satisfactory insulating material, where dimensional instability and linear shrinkage of the foam occurs.
Conventional urea-formaldehyde foams start to lose their dimensional integrity about as soon as drying is complete. The most damaging aspect of the loss of dimensional integrity is shrinkage. Although depth shrinkage of contiguous foam insulating blocks causes some reduction in insulating effectiveness, linear shrinkage is still more damaging. Linear shrinkage normally opens cracks in or around contiguous blocks or pieces of foam and creates insulation by-passes where heat or sound easily flow, thus destroying the effectiveness of the insulation.
It is therefore a primary object of this invention to provide a method of producing a substantially dimensionally stable urea-formaldehyde insulating foam.
It is another object of this invention to provide a method for modifying urea-formaldehyde foam to produce a substantially non-shrinking insulating foam.
It is still another object of this invention to provide a method for modifying urea-formaldehyde foams to increase physical integrity and strength.
These and other objects will be evident from the following description of the invention.